1. Field of the Invention
The present invention generally relates to communication systems, and more specifically to auto-negotiation in a communication system.
2. Background Art
High speed data links transmit data from one location to another over transmission lines. For example, an Ethernet data link is a well-known high speed data link, and IEEE Std. 802.3 defines an Ethernet standard.
Many Ethernet devices support a protocol handshake method defined by IEEE Std. 802.3 Clause 28, known generally as “auto-negotiation.” Auto-negotiation allows Ethernet (802.3) devices of various capabilities to discover each other and to communicate based on a common capability. Each device advertises its own capabilities and matches to the advertised capabilities of its link partner.
Clause 28 allows communication between some devices advertising a protocol other than 802.3. For example, devices advertising IEEE Std. 802.5 capability or devices advertising IEEE Std. 802.9 capability can communicate under Clause 28.
However, Clause 28 does not allow any device to simultaneously advertise both the ability to support 802.3 and the ability to support an alternate protocol. Clause 28 requires each device to set its Selector Field to either 802.3 or an alternate protocol, but not both.
Moreover, Clause 28 specifies that auto-negotiation occurs over a particular communication link (e.g., wire pairs A and B) between the devices. No uses are provided under Clause 28 for other communication links (e.g., wire pairs C and D) between the devices.
Thus, there is a need for a method and apparatus for auto-negotiation in a communication system that allows use of a second communication link to facilitate auto-negotiation of a second type.